Process for sweetening a sour hydrocarbon fraction using a solid base

ABSTRACT

A process for treating a hydrocarbon fraction which contains mercaptans has been developed. The process uses a novel catalyst which is composed of a metal chelate dispersed on a basic support which is either a solid solution of metal oxides or a layered double hydroxide (LDH). In the process the hydrocarbon fraction is contacted with the catalyst in the presence of an oxidizing agent and a polar compound. Examples of these polar compounds are water and alcohols, with methanol being especially preferred. The process is unique in that the solid solution or LDH are solid bases which eliminates the need for a liquid base. Optionally, an onium compound may be used as a catalyst promoter.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of prior copendingapplication Ser. No. 07/862,151 filed on Apr. 2, 1992, now U.S. Pat. No.5,232,887 by Aug. 4, 1993.

BACKGROUND OF THE INVENTION

Processes for the treatment of a sour hydrocarbon fraction where thefraction is treated by contacting it with an oxidation catalyst and analkaline agent in the presence of an oxidizing agent at reactionconditions have become well known and widely practiced in the petroleumrefining industry. These processes are typically designed to effect theoxidation of offensive mercaptans contained in a sour hydrocarbonfraction to innocuous disulfides--a process commonly referred to assweetening. The oxidizing agent is most often air. Gasoline, includingnatural, straight run and cracked gasolines, is the most frequentlytreated sour hydrocarbon fraction. Other sour hydrocarbon fractionswhich can be treated include the normally gaseous petroleum fractions aswell as naphtha, kerosene, jet fuel, fuel oil, and the like.

A commonly used continuous process for treating sour hydrocarbonfractions entails contacting the fraction with a metal phthalocyaninecatalyst dispersed in an aqueous caustic solution to yield a doctorsweet product. Doctor sweet means a mercaptan content in the product lowenough to test "sweet" (as opposed to "sour") by the well known doctortest. The sour fraction and the catalyst containing aqueous causticsolution provide a liquid-liquid system wherein mercaptans are convertedto disulfides at the interface of the immiscible solutions in thepresence of an oxidizing agent--usually air. Sour hydrocarbon fractionscontaining more difficult to oxidize mercaptans are more effectivelytreated in contact with a metal chelate catalyst dispersed on a highsurface area adsorptive support--usually a metal phthalocyanine on anactivated charcoal. The fraction is treated by contacting it with thesupported metal chelate catalyst at oxidation conditions in the presenceof a soluble alkaline agent. One such process is described in U.S. Pat.No. 2,988,500. The oxidizing agent is most often air admixed with thefraction to be treated, and the alkaline agent is most often an aqueouscaustic solution charged continuously to the process or intermittentlyas required to maintain the catalyst in the caustic-wetted state.

The prior art shows that alkaline agents are necessary in order tocatalytically oxidize mercaptans to disulfides. Thus, U.S. Pat. Nos.3,108,081 and 4,156,641 disclose the use of alkali hydroxides especiallysodium hydroxide for oxidizing mercaptans. Further, U.S. Pat. No.4,913,802 discloses the use of ammonium hydroxide as the basic agent.The activity of the metal chelate systems can be improved by the use ofquaternary ammonium compound as disclosed in U.S. Pat. Nos. 4,290,913and 4,337,147.

Applicants have developed a catalyst and a process using the catalystwhich is completely different from all the sweetening processespreviously disclosed in the art. Applicant's process involves the use ofa solid base instead of a liquid base. The solid bases which can be usedto carry out the instant process are either a solid solution of metaloxides or layered double hydroxides (LDH). One example of a solidsolution of metal oxides is magnesium oxide and aluminum oxide withvarying Mg/Al ratios. An example of a layered double hydroxide ishydrotalcite which is a clay having the formula Mg₆ Al₂ (OH)₁₆ (CO₃)·4H₂O. Applicants have also found that these solid bases can serve as thesupport for the desired metal chelate. In order to obtain appreciableconversion of mercaptans to disulfides applicants have furtherdetermined that an effective amount of a polar compound capable ofserving as a proton-transfer medium must be added to the process.Examples of these compounds are water and methanol.

To applicant's knowledge there is only one report in the literature of ahydrotalcite material being used to oxidize mercaptans. CatalysisLetters11, pp. 55-62 (1991). This article describes the oxidation of1-decanethiol in water. However, the catalyst and process described inthis article are considerably different from applicant's process andcatalyst. The reference discloses an LDH in which cobalt phthalocyanineis intercalated between the LDH layers, whereas applicant's compositionis a metal chelate, e.g., cobalt phthalocyanine dispersed on an LDHsupport. The reference uses a borate buffer to maintain the pH at 9.25whereas applicants do not use any added base. Thus, the system disclosedin the reference and applicants' system are clearly different.

Finally, it should be pointed out that the prior art discloses thatmetal chelates can be dispersed on adsorbent supports such as clays oroxides (see e.g., U.S. Pat. No. 4,290,913). However, there is noindication that solid solutions or LDHs could be used as support northat such catalysts would be able to function without an added liquidbase.

SUMMARY OF THE INVENTION

As stated, this invention relates to a process for treating a sourhydrocarbon fraction containing mercaptans and to a catalyst for use insaid process. One embodiment of the invention is a catalyst foroxidizing mercaptans to disulfides comprising a metal chelate dispersedon a support selected from the group consisting of a solid solution ofmetal oxides, a layered double hydroxide and mixtures thereof, the solidsolution having the formula xMO·yM'₂ O₃ where M is at least one metalhaving a +2 oxidation state and is selected from the group consisting ofmagnesium, nickel, zinc, copper, iron, cobalt, calcium and mixturesthereof and M' is at least one metal having a +3 oxidation state and isselected from the group consisting of aluminum, chromium, gallium,scandium, iron, lanthanum, cerium, yttrium, boron and mixtures thereofand the ratio of x:y is greater than 1 to about 15, the layered doublehydroxide represented by the formula

    M.sub.x M'y(OH).sub.2x+2y (X.sup.-)y·zH.sub.2 O

where X⁻ is an anion selected from the group consisting of carbonate,nitrate, halide and mixtures thereof, the ratio of x:y is greater than 1to about 15, and z varies from about 1 to about 50.

Another embodiment of the invention is a process for sweetening a sourhydrocarbon fraction which involves contacting the sour hydrocarbonfraction with the catalyst described in the previous paragraph in thepresence of an oxidizing agent and an effective amount of a polarcompound.

A specific embodiment of the invention is a catalyst containing cobaltphthalocyanine on a magnesium oxide/aluminum oxide (Mg/Al ratio of 2:1)support. This catalyst is used in conjunction with air and methanol tosweeten a sour hydrocarbon fraction.

Other objects and embodiments of this invention will become apparent inthe following detailed description.

DETAILED DESCRIPTION OF THE INVENTION

As stated, this invention relates to a process for treating a sourhydrocarbon fraction that contains mercaptans and to a catalyst for usein said process. The process involves contacting the hydrocarbonfraction with a catalyst, which is a metal chelate dispersed on a solidbase, in the presence of an oxidizing agent and an effective amount of apolar compound.

Thus, one necessary component of the instant invention is a metalchelate. The metal chelate employed in the practice of this inventioncan be any of the various metal chelates known to the art as effectivein catalyzing the oxidation of mercaptans contained in a sour petroleumdistillate to disulfides. The metal chelates include the metal compoundsof tetrapyridinoporphyrazine described in U.S. Pat. No. 3,980,582, e.g.,cobalt tetrapyridinoporphyrazine; porphyrin and metaloporphyrincatalysts as described in U.S. Pat. No. 2,966,453, e.g., cobalttetraphenylporphyrin sulfonate; corrinoid catalysts as described in U.S.Pat. No. 3,252,892, e.g., cobalt corrin sulfonate; chelateorganometallic catalysts such as described in U.S. Pat. No. 2,918,426,e.g., the condensation product of an aminophenol and a metal of GroupVIII; and the metal phthalocyanines as described in U.S. Pat. No.4,290,913, etc. As stated in U.S. Pat. No. 4,290,913, metalphthalocyanines are a preferred class of metal chelates.

The metal phthalocyanines which can be employed to catalyze theoxidation of mercaptans generally include magnesium phthalocyanine,titanium phthalocyanine, hafnium phthalocyanine, vanadiumphthalocyanine, niobium phthalocyanine, tantalum phthalocyanine,molybdenum phthalocyanine, manganese phthalocyanine, ironphthalocyanine, cobalt phthalocyanine, nickel phthalocyanine, platinumphthalocyanine, palladium phthalocyanine, copper phthalocyanine, silverphthalocyanine, zinc phthalocyanine, tin phthalocyanine, and the like.Cobalt phthalocyanine and vanadium phthalocyanine are particularlypreferred. The ring substituted metal phthalocyanines are generallyemployed in preference to the unsubstituted metal phthalocyanine (seeU.S. Pat. 4,290,913), with the sulfonated metal phthalocyanine beingespecially preferred, e.g., cobalt phthalocyanine monosulfate, cobaltphthalocyanine disulfonate, etc. The sulfonated derivatives may beprepared, for example, by reacting cobalt, vanadium or other metalphthalocyanine with fuming sulfuric acid. While the sulfonatedderivatives are preferred, it is understood that other derivatives,particularly the carboxylated derivatives, may be employed. Thecarboxylated derivatives are readily prepared by the action oftrichloroacetic acid on the metal phthalocyanine.

Another necessary component of this invention is a solid base which alsoacts as the support for the metal chelate. The solid base can be a solidsolution of metal oxides, a layered double hydroxide or a mixturethereof. The solid solution has the formula xMO·yM'₂ O₃ where M is ametal with a +2 oxidation state and M' is a metal with a +3 oxidationstate. The M metals are selected from the group consisting of magnesium,nickel, zinc, copper, iron, cobalt and mixtures thereof, while M' isselected from the group consisting of aluminum, chromium, gallium andmixtures thereof. Finally, x and y are chosen such that the ratio of x:yis greater than one to about 15. These solid solution materials areprepared by heating the corresponding layered double hydroxide (LDH)materials at a temperature of about 300° to about 750° C. When preparingthe solid solution from the LDH precursor, the precursor must have asits counter ion (anion) one which decomposes upon heating, e.g., nitrateor carbonate. Counter ions such as chloride or bromide would be left onthe solid solution support and may be detrimental to catalyst activity.

Layered double hydroxides (LDH) are basic materials that have theformula

    M.sub.x M'y(OH).sub.2x+2y (X.sup.-)y·zH.sub.2 O

The M and M' metals are the same as those described for the solidsolution. The values of x and y are also as set forth above. X⁻ is ananion selected from the group consisting of carbonate, nitrate, halidesand mixtures thereof with carbonate and nitrate preferred. Finally, zvaries from about 1 to about 50 and preferably from about 1 to about 15.These materials are referred to as layered double hydroxides becausethey are composed of octahedral layers, i.e. the metal cations areoctahedrally surrounded by hydroxyl groups. These octahedra share edgesto form infinite sheets. Interstitial anions such as carbonate arepresent to balance the positive charge in the octahedral layers. Thepreparation of layered double hydroxides is well known in the art andcan be exemplified by the preparation of a magnesium/aluminum layereddouble hydroxide which is known as hydrotalcite. Hydrotalcite can beprepared by coprecipitation of magnesium and aluminum carbonates at ahigh pH. Thus magnesium nitrate and aluminum nitrate (in the desiredratios) are added to an aqueous solution containing sodium hydroxide andsodium carbonate. The resultant slurry is heated at about 65° C. tocrystallize the hydrotalcite and then the powder is isolated and dried.Extensive details for the presentation of various LDH materials may befound in J. Catalysis, 94, 547-557 (1985) which is incorporated byreference.

Although both the LDH and the basic solid solutions can be used as thesolid base and support, it is preferred to use the solid solutions. Onereason is that the solid solutions have a much higher surface area thanthe LDH materials, usually on the order of about 150 to about 350 m² /gversus less than 100 m² /g for the LDH materials. Owing to thisincreased surface area, the basic sites are more accessible in the solidsolution than in the LDH. Additionally, the LDH has some counterion suchas carbonate and therefore has few true basic sites. That is, theability of the LDH to exchange anions is owing to the presence of theanions and not the presence of true basic sites.

The metal chelate component can be dispersed on the solid base supportin any conventional or otherwise convenient manner. The metal chelatecan be dispersed on the support from an aqueous or alcoholic solutionand/or dispersion thereof. The dispersion process can be effectedutilizing conventional techniques whereby the support in the form ofspheres, pills, pellets, granules or other particles of uniform orirregular size or shape, is soaked, suspended, dipped one or more times,or otherwise immersed in an aqueous or alcoholic, e.g. methanol,solution and/or dispersion to disperse a given quantity of the metalchelate. It is preferred to use an alcoholic solution. In general, theamount of metal chelate which can be adsorbed on the solid base supportand still form a stable catalyst is up to about 25 weight percent of thecomposite. A lesser amount in the range of from about 0.1 to about 10weight percent of the composite generally forms a suitably activecatalyst.

One method of preparation involves the use of a steam-jacketed rotarydryer. The solid base support is immersed in the impregnating solutionand/or dispersion containing the desired metal chelate contained in thedryer and the support is tumbled therein by the rotating motion of thedryer. Evaporation of the solution in contact with the tumbling supportis expedited by applying steam to the dryer jacket. In any case, theresulting composite is allowed to dry under ambient temperatureconditions, or dried at an elevated temperature in an oven, or in a flowof hot gases, or in any other suitable manner.

It is important to point out that the metal chelate is impregnated ontothe LDH and not intercalated. Impregnation results in a more activecatalyst since intercalation stuffs the layer with the metal chelatethereby making it difficult for mercaptan molecules to get to the metalcenter.

In order to improve the activity and stability of the catalyst, an oniumcompound can be added to the hydrocarbon feed or can be dispersed on thehydrotalcite along with the metal chelate. Onium compounds are ioniccompounds in which the positively charged (cationic) atom is anonmetallic element, other than carbon, not bonded to hydrogen. Theonium compounds which can be used in this invention are selected fromthe group consisting of phosphonium, ammoniun, arsonium, stibonium,oxonium and sulfonium compounds, i.e., the cationic atom is phosphorus,nitrogen, arsenic, antimony, oxygen and sulfur, respectively. Table 1presents the general formula of these onium compounds, and the cationicelement.

                  TABLE 1                                                         ______________________________________                                        Name and Formula of Onium Compounds                                           Formula*   Name            Cationic Element                                   ______________________________________                                        R.sub.4 N.sup.+                                                                          quaternary ammonium                                                                           nitrogen                                           R.sub.4 P.sup.+                                                                          phosphonium     phosphorous                                        R.sub.4 As.sup.+                                                                         arsonium        arsenic                                            R.sub.4 Sb.sup.+                                                                         stibonium       antimony                                           R.sub.3 O.sup.+                                                                          oxonium         oxygen                                             R.sub.3 S.sup.+                                                                          sulfonium       sulfur                                             ______________________________________                                         *R is a hydrocarbon radical.                                             

For the practice of this invention it is desirable that the oniumcompounds have the general formula [R'(R)_(W) M]⁺ X⁻. In said formula, Ris a hydrocarbon group containing up to about 20 carbon atoms andselected from the group consisting of alkyl, cycloalkyl, aryl, alkaryland aralkyl. It is preferred that one R group be an alkyl groupcontaining from about 10 to about 18 carbon atoms. The other R group(s)is (are) preferably methyl, ethyl, propyl, butyl, benzyl, phenyl andnaphthyl groups. R' is a straight chain alkyl group containing fromabout 5 to about 20 carbon atoms and preferably an alkyl radicalcontaining about 10 to about 18 carbon atoms, X is hydroxide, sulfate,nitrate, nitrite, phosphate, acetate, citrate and tartrate, and w is 2when M is oxygen or sulfur and w is 3 when M is phosphorus, nitrogen,arsenic or antimony. The preferred cationic elements are phosphorus,nitrogen, sulfur and oxygen.

Illustrative examples of onium compounds which can be used to practicethis invention, but which are not intended to limit the scope of thisinvention are: benzyldiethyldodecylphosphonium hydroxide,phenyldimethyldecylphosphonium hydroxide, benzyldibutyldecylphosphoniumhydroxide, benzyldimethylhexadecylphosphonium hydroxide,trimethyldodecylphosphonium hydroxide,naphthyldimethylhexadecylphosphonium hydroxide,tributylhexadecylphosphonium hydroxide, benzylmethylhexadecyloxoniumhydroxide, benzylethyldodecyloxonium hydroxide,naphthylpropyldecyloxonium hydroxide, dibutyldodecyloxonium hydroxide,phenylmethyldodecyloxonium hydroxide, dipropylhexadecyloxoniumhydroxide, dibutylhexadecyloxonium hydroxide,benzylmethylhexadecylsulfonium hydroxide, diethyldodecylsulfoniumhydroxide, naphthylpropylhexadecylsulfonium hydroxide,phenylmethylhexadecylsulfonium hydroxide, dimethylhexadecylsulfoniumhydroxide, benzylbutyldodecylsulfonium hydroxide,benzyldiethyldodecylarsonium hydroxide, benzyldiethyldodecylstiboniumhydroxide, trimethyldodecylarsonium hydroxide, trimethyldodecylstiboniumhydroxide, benzyldibutyldecylarsonium hydroxide,benzyldibutyldecylstibonium hydroxide, tributylhexadecylarsoniumhydroxide, tributylhexadecylstibonium hydroxide,naphthylpropyldecylarsonium hydroxide, naphthylpropyldecylstiboniumhydroxide, benzylmethylhexadecylarsonium hydroxide,benzylmethylhexadecylstibonium hydroxide, benzylbutyldodecylarsoniumhydroxide, benzylbutyldodecylstibonium hydroxide,benzyldimethyldodecylammonium hydroxide,benzyldimethyltetradecylammonium hydroxide,benzyldimethylhexadecylammonium hydroxide,benzyldimethyloctadecylammonium hydroxide,dimethylcyclohexyloctylammonium hydroxide,diethylcyclohexyloctylammonium hydroxide,dipropylcyclohexyloctylammonium hydroxide,dimethylcyclohexyldecylammonium hydroxide,diethylcyclohexyldecylammonium hydroxide, hydroxide,dipropylcylohexyldecylammonium hydroxide,dimethylcyclohexyldodecylammonium hydroxide,diethylcyclohexyldodecylammonium hydroxide,dipropylcyclohexyldodecylammonium hydroxide,dimethylcyclohexyltetradecylammonium hydroxide,diethylcyclohexyltetradecylammonium hydroxide,dipropylcyclohexyltetradecylammonium hydroxide,dimethylcyclohexylhexadecylammonium hydroxide,diethylcyclohexylhexadecylammonium hydroxide,dipropylcyclohexylhexadecylammonium hydroxide,dimethylcyclohexyloctadecylammonium hydroxide,diethylcyclohexyloctadecylammonium hydroxide,dipropylcyclohexyloctadecylammonium hydroxide, as well as thecorresponding sulfate, nitrate, nitrite, phosphate, acetate, citrate andtartrate. Other suitable quaternary ammonium hydroxides are described inU.S. Pat. No. 4,156,641, which is incorporated by reference.

When the optional onium compound is added as a liquid to the hydrocarbonfraction, it is desirable that it be present in a concentration fromabout 0.05 to about 500 wppm and preferably from about 0.5 wppm to about100 wppm based on hydrocarbon. If it is desired to disperse the oniumcompound onto the hydrotalcite support, this may be done as describedfor the metal chelate. The onium compound may be impregnated either froma separate solution before or after the impregnation of the metalchelate or it may be impregnated from a common solution. When the oniumcompound is dispersed onto the hydrotalcite support, it is desirablethat it be present in a concentration from about 0.1 to about 10 weightpercent of the catalyst. Of course as is well known in the art, theonium compound may be initially dispersed onto the hydrotalcite and thendesired amounts within the stated range above added intermittently tothe hydrocarbon fraction.

An alternative and convenient method for dispersing the metal chelateand optional onium compound on the basic support comprises predisposingthe support in a sour hydrocarbon fraction treating zone or chamber as afixed bed and passing a metal chelate and optional onium compoundsolution and/or dispersion through the bed in order to form thecatalytic composite in situ. This method allows the solution and/ordispersion to be recycled one or more times to achieve a desiredconcentration of the metal chelate and optional onium compound on theadsorbent support. In still another alternative method, the basicsupport may be predisposed in said treating zone or chamber, and thezone or chamber thereafter filled with the solution and/or dispersion tosoak the support for a predetermined period.

Another necessary component of the process of this invention is a polarcompound. It is believed that the function of this polar compound is toserve as a proton transfer medium. Specifically the compound is selectedfrom the group consisting of water, alcohols, esters, ketones, diols andmixtures thereof. Specific examples include methanol, ethanol, propanol,isopropanol, t-butanol, n-butanol, benzyl alcohol and s-butanol.Examples of diols which can be used include ethylene glycol,1,3-propylene glycol, 1,2-propylene glycol, 1,4-butylene glycol,1,3-butylene glycol and 2,3-butylene glycol. Examples of ketones andesters are acetone, methyl formate and ethyl acetate. Of these compoundspreferred compounds are water and alcohols, with methanol being anespecially preferred alcohol.

As previously stated, sweetening of the sour hydrocarbon fraction iseffected by oxidizing the mercaptans to disulfides. Accordingly, theprocess requires an oxidizing agent, preferably air, although oxygen orother oxygen-containing gases may be employed. The sour hydrocarbonfraction may contain sufficient entrained air, but generally added airis admixed with the fraction and charged to the treating zoneconcurrently therewith. In some cases, it may be advantageous to chargethe air separately to the treating zone and countercurrent to thefraction separately charged thereto.

The treating conditions and specific methods used to carry out thepresent invention are those that have been disclosed in the prior art.Typically, the sour hydrocarbon fraction is contacted with the catalystwhich is in the form of a fixed bed. The contacting is thus carried outin a continuous manner and the hydrocarbon fraction may be flowedupwardly or downwardly through the catalytic composite. The process isusually effected at ambient temperature conditions, although highertemperatures up to about 105° C. are suitably employed. Pressures of upto about 1,000 psi or more are operable although atmospheric orsubstantially atmospheric pressures are suitable. Contact timesequivalent to a liquid hourly space velocity of from about 0.5 to about10 or more are effective to achieve a desired reduction in the mercaptancontent of a sour hydrocarbon fraction, an optimum contact time beingdependent on the size of the treating zone, the quantity of catalystcontained therein, and the character of the fraction being treated.Examples of specific arrangements to carry out the treating process maybe found in U.S. Pat. Nos. 4,490,246 and 4,753,722 which areincorporated by reference.

The following examples are presented in illustration of this inventionand are not intended as undue limitations on the generally broad scopeof the invention as set out in the appended claims.

EXAMPLE 1 Preparation of MgO·Al₂ O₃ Solid Solution.

A 2L, 3-necked round bottomed flask was equipped with a refluxcondenser, a thermometer, a mechanical stirrer, and a Glass Col™ heatingmantle. To this 3-neck flask there was added a solution containing 610 gof water, 60 g of Na₂ CO₃ ·H₂ O and 71 g of NaOH and the flask wascooled to less than 5° C. An addition funnel was put in place of thereflux condenser and charged with a solution of 345 g water, 130 gMg(NO₃)₂ ·6H₂ O and 75 g Al(NO₃)₃ ·9H₂ O. This solution was added over aperiod of 4 hours while maintaining the reaction mixture temperature atless than 5° C. The resultant slurry was stirred for 1 hour at less than5° C. The addition funnel was removed and the reflux condenser replacedin order to heat the slurry to 60° C.±5° C. for 1 hour. The slurry wasthen cooled to room temperature and the solids recovered by filtration,washed with 10 L of hot DI water and then dried at 100° C. for 16 hours.After crushing, the solid material was slurried and extruded. Thisproduct was characterized as an LDH by its x-ray diffraction (XRD)pattern. The extruded product was calcined at 450° C. for 12 hours in amuffle furnace with an air flow. This product was characterized as aMgO·Al₂ O₃ solid solution by XRD. The BET surface area for this materialwas 240 m² /g.

EXAMPLE 2 Preparation of Cobalt Phthalocyanine on MgO·Al₂ O₃ Catalyst.

To 50 mL of methanol there were added 0.60 g of cobalt phthalocyaninetetrasulfonate, prepared as described in U.S. Pat. No. 4,003,827, togive a deep blue homogeneous solution. To this solution there were added16 g of the MgO/Al₂ O₃ solid solution extrudate prepared in Example 1.The resultant mixture was agitated gently for about 16 hours andfiltered. The solid material which was now a deep blue was washed threetimes with 30 mL of fresh methanol and then dried at 110° C. for onehour. Analysis of this material indicated that it contained 750 ppm ofcobalt. This sample was identified as catalyst A and had an x-raydiffraction pattern characteristic of cobalt phthalocyanine on a MgO·Al₂O₃. solid solution.

EXAMPLE 3

A reactor bed was filled with 17 cc of catalyst A. A sour kerosenefeedstock boiling in the 48°-228° C. and containing about 162 ppmmercaptan sulfur was processed downflow through the reactor bed at aliquid hourly space velocity of 1.2, an inlet temperature of 38° C. anda pressure of 100 psig. The feedstock was charged under sufficient airpressure to provide about 1.3 times the stoichiometric amount of oxygenrequired to oxidize the mercaptans.

For the first 110 hours on streams no water was added to the kerosenefeed. Although the catalyst had good initial activity (product had only10 ppm mercaptan), at about 110 hours the product had 90 ppm mercaptan.At this point 7,000 ppm of water was added to the feed and the mercaptanlevel monitored. The results of this test are presented in Table 2.

                  TABLE 2                                                         ______________________________________                                        Mercaptan Conversion Using a Cobalt Phthalocyanine                            on MgO/Al.sub.2 O.sub.3 Catalyst and Water                                    Time on       Product Mercaptan                                               Stream (Hrs)  Sulfur (WPPM)                                                   ______________________________________                                        112           89                                                              120           53                                                              136           12                                                              152           11                                                              168           11                                                              200           16                                                              224           22                                                              248           30                                                              ______________________________________                                    

As the data show, the catalyst of this invention (catalyst A) is able tosweeten a sour kerosine feed for a considerable amount of time on streamwith deterioration being observed only at the tail end of the run.

EXAMPLE 4

The process described in Example 3 was repeated using a fresh batch ofcatalyst A and using methanol instead of water. The results of thisexperiment are presented in Table 3.

                  TABLE 3                                                         ______________________________________                                        Mercaptan Conversion Using Cobalt Phthalocyanine                              on MgO/Al.sub.2 O.sub.3 Catalyst and Methanol                                 Time on      Methanol   Product Mercaptan                                     Stream (Hrs) Conc. (ppm)                                                                              Sulfur (WPPM)                                         ______________________________________                                         8           8,400      60                                                     24          8,400      31                                                     40          8,400      20                                                     56          4,200      18                                                     80          4,200      18                                                    104          4,200      16                                                    128          4,200      15                                                    152          4,200      12                                                    160          2,100      11                                                    184          2,100      14                                                    ______________________________________                                    

Again, the data clearly show the ability of a catalyst of this inventionto sweeten a sour hydrocarbon fraction when methanol is used as thepolar compound.

We claim as our invention:
 1. A process for sweetening a sour hydrocarbon fraction containing mercaptans comprising contacting the hydrocarbon fraction in the presence of an oxidizing agent with a catalyst and an effective amount of a polar compound, the catalyst comprising a metal chelate dispersed on a support selected from the group consisting of a solid solution of metal oxides, a layered double hydroxide and mixtures thereof, the solid solution having the formula xMO·yM'₂ O₃ where M is at least one metal having a +2 oxidation state and is selected from the group consisting of magnesium, nickel, zinc, copper, iron, cobalt and mixtures thereof and M' is at least one metal having a +3 oxidation state and is selected from the group consisting of aluminum, chromium, gallium, scandium, iron, lanthanum, cerium, yttrium, boron and mixtures thereof and the ratio of x:y is greater than 1 to about 15, the layered double hydroxide represented by the formula

    M.sub.x M'y(OH).sub.2x+2y (X.sup.-)y·zH.sub.2 O

where X⁻ is an anion selected from the group consisting of carbonate, nitrate, halide and mixtures thereof, M and M' metals are the same as those described for the solid solution, the ratio of x:y is greater than 1 to about 15, and z varies from about 1 to about 50, thereby oxidizing the mercaptans to disulfides.
 2. The process of claim 1 where the polar compound is selected from the group consisting of water, alcohols, diols, esters, ketones and mixtures thereof.
 3. The process of claim 1 where the polar compound is present in a concentration from about 10 ppm to about 15,000 ppm based on hydrocarbon.
 4. The process of claim 2 where the polar compound is water.
 5. The process of claim 2 where the polar compound is an alcohol selected from the group consisting of methanol, t-butanol, n-butanol, ethanol, propanol, isopropanol, benzyl alcohol, s-butanol, and mixtures thereof.
 6. The process of claim 5 where the alcohol is methanol.
 7. The process of claim 1 where the support is a solid solution of metal oxides.
 8. The process of claim 7 where the solid solution is a magnesium oxide and aluminum oxide solid solution.
 9. The process of claim 1 where the support is a layered double hydroxide.
 10. The process of claim 1 where the metal chelate is a metal phthalocyanine.
 11. The process of claim 10 where the metal phthalocyanine is cobalt phthalocyanine.
 12. The process of claim 1 where the metal chelate is present in a concentration from about 0.1 to about 10 weight percent of the catalyst.
 13. The process of claim 1 further characterized in that said hydrocarbon fraction is also contacted with an onium compound having the formula [R'(R)_(w) M]⁺ X⁻ where R is a hydrocarbon group containing up to about 20 carbon atoms and selected from the group consisting of alkyl, cycloalkyl, aryl, alkaryl and aralkyl, R' is a straight chain alkyl group containing from about 5 to about 20 carbon atoms, M is phosphorus (phosphonium compound), nitrogen (ammonium compound), arsenic (arsonium compound), antimony (stibonium compound), oxygen (oxonium compound) or sulfur (sulfonium compound), X is hydroxide, sulfate, nitrate, nitrite, phosphate, acetate, citrate and tartrate, w is 2 when M is oxygen or sulfur and w is 3 when M is phosphorous, nitrogen, arsenic or antimony.
 14. The process of claim 13 where the onium compound is a quaternary ammonium compound.
 15. The process of claim 13 where the onium compound is added to the hydrocarbon and is present in a concentration of about 0.05 to about 500 wppm.
 16. The process of claim 13 where the onium compound is dispersed onto the support and is present in a concentration of about 0.1 to about 10 weight percent of the catalyst. 